Realistically, this is what I would do (I work on something very similar but not really in adtech space):
1. Load data in text form (assuming it sits in S3) inside hadoop (EMR/Spark)
2. Generate reports you need based on your data and cache them in mysql RDS.
3. Serve the pre-generated reports to your user. You can get creative here and generate bucketed reports where user will fill its more "interactive". This approach will take you a long way and when you have time/money/people, maybe you can try getting fancier and better.
Getting fancy: If you truly want near-real time querying capabilities I would looks at apache kylin or linkedin pinot. But I would stay away from those for now.
Bigtable: As someone pointed out, bigtable is good solution (although I haven't used it) but since you are on AWS ecosystem, I would stick there.